What is the difference between overloading and overriding.
This question is related to
c#
inheritance
Overloading
Overloading is when you have multiple methods in the same scope, with the same name but different signatures.
//Overloading
public class test
{
public void getStuff(int id)
{}
public void getStuff(string name)
{}
}
Overriding
Overriding is a principle that allows you to change the functionality of a method in a child class.
//Overriding
public class test
{
public virtual void getStuff(int id)
{
//Get stuff default location
}
}
public class test2 : test
{
public override void getStuff(int id)
{
//base.getStuff(id);
//or - Get stuff new location
}
}
Another point to add.
Overloading More than one method with Same name. Same or different return type. Different no of parameters or Different type of parameters. In Same Class or Derived class.
int Add(int num1, int num2) int Add(int num1, int num2, int num3) double Add(int num1, int num2) double Add(double num1, double num2)
Can be possible in same class or derived class. Generally prefers in same class. E.g. Console.WriteLine() has 19 overloaded methods.
Can overload class constructors, methods.
Can consider as Compile Time (static / Early Binding) polymorphism.
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Overriding cannot be possible in same class. Can Override class methods, properties, indexers, events.
Has some limitations like The overridden base method must be virtual, abstract, or override. You cannot use the new, static, or virtual modifiers to modify an override method.
Can Consider as Run Time (Dynamic / Late Binding) polymorphism.
Helps in versioning http://msdn.microsoft.com/en-us/library/6fawty39.aspx
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Helpful Links
http://msdn.microsoft.com/en-us/library/ms173152.aspx Compile time polymorphism vs. run time polymorphism
in C# there is no Java like hidden override, without keyword override on overriding method! see these C# implementations:
variant 1 without override: result is 200
class Car {
public int topSpeed() {
return 200;
}
}
class Ferrari : Car {
public int topSpeed(){
return 400;
}
}
static void Main(string[] args){
Car car = new Ferrari();
int num= car.topSpeed();
Console.WriteLine("Top speed for this car is: "+num);
Console.ReadLine();
}
variant 2 with override keyword: result is 400
class Car {
public virtual int topSpeed() {
return 200;
}
}
class Ferrari : Car {
public override int topSpeed(){
return 400;
}
}
static void Main(string[] args){
Car car = new Ferrari();
int num= car.topSpeed();
Console.WriteLine("Top speed for this car is: "+num);
Console.ReadLine();
}
keyword virtual on Car class is opposite for final on Java, means not final, you can override, or implement if Car was abstract
Overloading is the concept in which you have same signatures or methods with same name but different parameters and overriding, we have same name methods with different parameters also have inheritance is known as overriding.
Overloading is a part of static polymorphism and is used to implement different method with same name but different signatures. Overriding is used to complete the incomplete method. In my opinion there is no comparison between these two concepts, the only thing is similar is that both come with the same vocabulary that is over.
Method overloading and Method overriding are 2 different concepts completely different. Method overloading is having the same method name but with different signatures. Method overriding is changing the default implementation of base class method in the derived class. Below you can find 2 excellent video tutorials explaining these concepts.
Simple definitions for overloading and overriding
Overloading (Compile Time Polymorphism):: Functions with same name and different parameters
public class A
{
public void print(int x, int y)
{
Console.WriteLine("Parent Method");
}
}
public class B : A
{
public void child()
{
Console.WriteLine("Child Method");
}
public void print(float x, float y)
{
Console.WriteLine("Overload child method");
}
}
Overriding (Run Time Polymorphism):: Functions in the extended class with same name and same parameters as in the base class, but with different behaviors.
public class A
{
public virtual void print()
{
Console.WriteLine("Parent Method");
}
}
public class B : A
{
public void child()
{
Console.WriteLine("Child Method");
}
public override void print()
{
Console.WriteLine("Overriding child method");
}
}
An astute interviewer would have followed up with:
Having more than one methods/constructors with same name but different parameters is called overloading. This is a compile time event.
Class Addition
{
int add(int a, int b)
{
return a+b;
}
int add(int a, int b, int c)
{
return a+b+c;
}
public static main (String[] args)
{
Addition addNum = new Addition();
System.out.println(addNum.add(1,2));
System.out.println(addNum.add(1,2,3));
}
}
O/p:
3
6
Overriding is a run time event, meaning based on your code the output changes at run time.
class Car
{
public int topSpeed()
{
return 200;
}
}
class Ferrari extends Car
{
public int topSpeed()
{
return 400;
}
public static void main(String args[])
{
Car car = new Ferrari();
int num= car.topSpeed();
System.out.println("Top speed for this car is: "+num);
}
}
Notice there is a common method in both classes topSpeed(). Since we instantiated a Ferrari, we get a different result.
O/p:
Top speed for this car is: 400
As Michael said:
and
I want to share an example which made a lot sense to me when I was learning:
This is just an example which does not include the virtual method or the base class. Just to give a hint regarding the main idea.
Let's say there is a Vehicle washing machine and it has a function called as "Wash" and accepts Car as a type.
Gets the Car input and washes the Car.
public void Wash(Car anyCar){
//wash the car
}
Let's overload Wash() function
Overloading:
public void Wash(Truck anyTruck){
//wash the Truck
}
Wash function was only washing a Car before, but now its overloaded to wash a Truck as well.
Let's override Wash() function
Overriding:
public override void Wash(Car anyCar){
//check if the car has already cleaned
if(anyCar.Clean){
//wax the car
}
else{
//wash the car
//dry the car
//wax the car
}
}
Wash function now has a condition to check if the Car is already clean and not need to be washed again.
If the Car is clean, then just wax it.
If not clean, then first wash the car, then dry it and then wax it
.
So the functionality has been overridden by adding a new functionality or do something totally different.
shadowing = maintains two definitions at derived class and in order to project the base class definition it shadowes(hides)derived class definition and vice versa.
Source: Stackoverflow.com